The present invention relates to a method for analyzing vapors generated from explosives, and an analysis apparatus for use in the method. More specifically, it relates to an analysis method and an analysis apparatus each preferably used for the stability test of an old explosive.
Deterioration of explosives due to secular changes and the like affects the aspect of performances, for example, in such a manner as to make a prescribed explosion power unobtainable. In addition, it increases the fear of causing spontaneous ignition or an incidental explosion accident. The explosives are affected by temperature, humidity, and light, and the speed of deterioration varies according to the storage state. Therefore, for explosives, it is difficult to understand the degree of its deterioration only by the length of time elapsed after manufacturing.
Conventionally, at the site of manufacturing and storage of explosives, examination of deterioration of explosives is carried out by the Abel heat test method. Below, a description will be given to the Abel heat test method adopting an explosive containing nitrate ester as an example by reference to FIGS. 9 and 10.
FIG. 9 is a schematic diagram of an apparatus 90 for carrying out the Abel heat test. A reference numeral 91 denotes a container for containing therein prescribed-temperature hot water. The container 91 includes a test tube 92 for filling therein an analysis sample, and a thermometer 93 for determining the bath hot water temperature. On the other hand, FIG. 10 is a schematic diagram for illustrating the test tube 92. The upper part of the test tube 92 is attached with a rubber stopper 94 including a glass rod 94a. The lower end of the glass rod 94a is provided with a potassium iodide starch paper 94c suspended from a platinum wire 94b in the form of key.
The Abel heat test method is carried out by means of the apparatus shown in FIGS. 9 and 10 in the following manner. First, a proper amount of the sample is collected into the test tube 92 as it is when the explosive containing nitrate ester of the sample is in granular form, or in small pieces when it is a large-size explosive in square, band, or string form or other form (not shown). When the sample has taken up moisture, previously, it is sufficiently dried by vacuum drying or the like at ordinary temperature, and then collected into the test tube 92. Subsequently, the test tube 92 is stopped by the rubber stopper 94 including the glass rod 94a having the test paper 94c. At this step, the upper half part of the test paper 94c is dampened with a half-and-half mixed solution of distilled water and glycerin. Subsequently, the test tube 92 is set in the apparatus 90 as shown in FIG. 9. Herein, a marked line 92a given on the test tube 92 in FIG. 10 denotes the critical position of the hot water bath upper surface when the test tube 92 is set in the apparatus 90, a marked line 92b denotes the actual hot water bath upper surface position, and a marked line 92c denotes the position at a height ⅓ of the height of the test tube 92. Whereas, in the container 91, a prescribed amount of prescribed-temperature, generally 65xc2x0 C. bath hot water is previously charged.
The analysis is carried out in the following manner. The test tube 92 is mounted at a prescribed position of the apparatus 90, and then, the length of time elapsed until the color tone with the same density as that of a standard paper occurs at the dry-wet boundary portion of the test paper 94c is determined. This determined time is taken as the heat resistant time, so that the deterioration states of explosives are determined according to this time.
Such a prior-art Abel heat test method has the following problems.
First, in the deterioration processes of explosives, predictably, there are present a process in which the explosives decompose while releasing nitrogen monoxide (NO) and a process in which the explosives decompose while releasing nitrogen dioxide (NO2). However, with the Abel heat test method, the amount of NO2 is determined, and hence sufficient attention has not been paid to NO. Further, in the determination of NO2 in the Abel heat test method, the criterion for deterioration is the value as very high as 200 ppm, so that the sensitivity is too low to examine the stability of the explosive in details. Still further, the analysis is carried out by a sensory test in which the color of the test paper in the test tube is visually judged. For this reason, another problem is unfavorably encountered that the differences in experience, color and temperature of the laboratory light source, and the like cause differences in results.
On the other hand, various methods have been used for general-purpose analysis of a chemical substance Among them, the mass spectrometry is known as an analysis method excellent in sensitivity and selectivity. With the mass spectrometry, ionization of a sample is required-for achieving the separation depending upon the mass to charge ratio (m/z). As the general-purpose ionization processes, mention may be made of: (a) a process by electron impact in a vacuum; (b) a process by the chemical reaction of primary ions and sample molecules; (c) a process utilizing the tunnel effect of electrons by an electric field; and (d) a process by impacts of neutral atoms at a solid phase interface.
The process (a) is excellent in ease of use and also in reproducibility. With the process (b), a difference in sensitivity is caused from one kind to another of samples according to the reactivity with the primary ions. With the process (c), a large amount of a sample is required, and further, the apparatus increases in size. With the process (d), a sample is easy to prepare, which enables the analysis of a high boiling sample.
However, these processes (a) to (d) are not necessarily sufficient for ionizing a vapor sample generated from explosives in a general manner.
In general, in order to identify a specific substance in a vapor mixture, the specific substance is required to be separated from the vapor mixture. As such a separation process, for example, gas chromatography/mass spectrometry (below, abbreviated as GC/MS) is known. This process is a system in which a specific substance is separated from a vapor mixture by GC, and analyzed by MS. However, with this process, a long time is taken for analysis, and hence it is difficult to continuously monitor the state of deterioration with time. In addition, operation and maintenance are required to be performed using a reference material at all times. Other analysis processes also present the same problems when using a separation means.
It is an object of the present invention to provide a method for analyzing vapors generated from explosives, capable of collecting a sample with ease, and stably analyzing the vapors generated from explosives in a short time and with high accuracy.
It is another object of the present invention to provide an apparatus for analyzing vapors generated from explosives, capable of analyzing the vapors generated from explosives in a short time and with high accuracy, and also capable of being reduced in size.
In accordance with the present invention, there is provided a method for analyzing vapors generated from explosives, which comprises: a step (1) of generating vapors from explosives; a step (2) of generating primary ions and neutral molecules from air; a step (3) of allowing the primary ions generated in the step (2) and an analysis target sample contained in the vapors generated in the step (1) to react with each other in an area inhibited or prevented from being penetrated by the neutral molecules generated in the step (2), and ionizing the sample; and a step (4) of subjecting the sample ionized in the step (3) to mass spectrometry.
In the step (1), as a process for generating vapors from explosives, for example, mention may be made of a process in which the explosives are heated to a desired temperature. The vapors to be generated include decomposition products from the explosives, for example, analysis target samples such as NO and NO2.
Herein, examples of the explosives which decompose to release NO and NO2 may include nitroglycol, nitroglycerin, pentaerythritol tetranitrate, trinitrotoluene, nitrocellulose, cyclotrimethylenetrinitroamine, and 2,4,6-trinitrophenylnitroamine. These explosives may be employed alone, or in mixture of two or more kinds thereof for use. Further, it is also possible to use explosives including other materials mixed therein.
The step (2) can be carried out, for example, in the following manner. A high voltage is applied to a needle electrode, so that a corona discharge is caused in the vicinity of the tip of the needle electrode. By the corona discharge, primary ions such as oxygen ions and neutral molecules of NO and the like are generated from air.
The step (3) is a step of allowing the primary ions generated in the step (2) and the analysis target sample contained in the vapors generated in the step (1) to react with each other, and ionizing the sample. In this step, if the vapors generated in the step (1) and the primary ions and the neutral molecules generated in the step (2) are allowed to react with each other in the same area, the high-accuracy analysis thereof becomes difficult. The reason for this is that it is not possible to distinguish the NO as the analysis target sample present in the vapors generated from explosives in the step (1) from the NO as the neutral molecules generated in the step (2).
Therefore, in the step (3) in the analysis method of the present invention, it is necessary to effect the reaction between the primary ions generated in the step (2) and the analysis target sample contained in the vapors generated in the step (1) in an area shielded from penetration of the neutral molecules generated in the step (2).
As a process for shielding the area from the neutral molecules, for example, mention may be made of the following process. As shown in FIG. 3 described later, the layout of an exhaust system is appropriately selected so that the neutral molecules can be inhibited or prevented from penetrating into the area where the primary ions and the analysis target sample react with each other. Thus, the flow of vapors generated in the step (1) and the flow of the neutral molecules are controlled. In addition, the reaction between the primary ions and the analysis target sample is effected by an atmospheric pressure ionization process. With such an atmospheric pressure ionization process, it is possible to continuously monitor the substances in the vapors, which enables the vapor components to be ionized in a short time and in a simple manner.
In the step (4), the mass spectrometry has no particular restriction. For example, the step (4) can be accomplished by a mass spectrometry employing a mass analyzer using a permanent magnet, a quadrupole mass analyzer, an ion trap mass analyzer, or the like.
Further, in accordance with the present invention, there is provided an apparatus for analyzing. vapors generated from explosives, which comprises: a vapor generating means for generating vapors from explosives; an atmospheric pressure ionization means for ionizing an analysis target sample contained in the vapors generated from the vapor generating means; and an analysis means for subjecting an ion sample obtained by the atmospheric pressure ionization means to mass spectrometry, characterized in that the atmospheric pressure ionization means includes a corona discharge unit for generating primary ions and neutral molecules; and an ionization reaction region for allowing the primary ions generated by the corona discharge unit and the analysis target sample to react with each other, and further includes a neutral molecule penetration inhibiting means for inhibiting or preventing the penetration of neutral molecules generated by a corona discharge in the ionization reaction region.